The supply of current consumers with electrical energy is no problem when these consumers are disposed close to electric power mains and when the structural complexity for connecting the consumers to the electrical power mains is possible with a reasonable effort.
However, in many cases, the connection of the small consumer to electric power mains is not possible because of the spatial distance from the power mains or also when extensive underground work is required in municipal areas.
It is generally known to operate such small consumers with a photovoltaic system when these small consumers are, for example, environmental measuring units, data units, safety units and mobile communications equipment on expressways or in open fields or these small consumers are illumination units, advertising units and marketing facilities in municipalities.
One such photovoltaic system is sold by Siemens AG and is described in the publication entitled “Transportation Systems” (TS RA PC ED2 PM) by Harald Walter, pages 1 to 5, 2002. This photovoltaic system includes a solar module which is mounted on a carrying mast secured in the ground. A switchgear cabinet is embedded in the ground at a spatial distance to this mast. The switchgear cabinet contains a control unit for supplying a consumer as needed and an energy store for taking up excessively generated energy and to output stored energy to the consumer. This switchgear cabinet is flush with the surface of the earth and has a cover for repair and maintenance purposes. Access to the control unit as well as the energy store is provided via the cover.
The control unit is functionally connected via an earth cable to the solar module and via internal cabling to the energy store. Furthermore, an earth cable leads to each spatially-remote consumer. This photovoltaic system can also be combined with one or several additional energy-generating systems via corresponding connections to the control unit. Energy-generating systems include, for example, a wind generator or a water generator.
This photovoltaic system has, however, disadvantages. First, the complexity of installation is very substantial because the solar mast as well as the switchgear cabinet and the corresponding consumers must be separately positioned and foundations prepared therefor. Making the foundation for the solar mast is very complex because it is subjected to considerable wind loads. The embedding of the switchgear cabinet in the ground is also very complex because a lot of earth must be moved. The complexity of installation is also increased by the required cabling in the ground. All this leads to an unreasonable installation cost which often bears no relationship to the use of the small consumers. Because of the high installation cost, this photovoltaic system can not be used in a portable manner. The installation complexity is further increased when the photovoltaic system is coupled to additional generators driven by wind or water because then also additional foundations and cabling are required.
Repair and maintenance work is very complicated because the control unit and the energy store are accessible only with difficulty and the control unit and energy store must be lifted to the surface from the depths of the switchgear cabinet so that they can be worked upon. This requires a very considerable bodily effort.
Also, an inadequate cooling of the energy store is a disadvantage because radiation heat emanating from the electronic components of the control unit cannot be conducted away and a temperature compensation can only take place via the ground. A controlled cooling of the energy store is not possible because the temperature of the ground is dependent upon the time of day and time of year and this cannot be influenced. This deteriorates the storage capacity of the energy store.
This photovoltaic system also does not satisfy the requirements as to safety because the above-earth solar module with its relatively thin solar mast as well as the below-ground switchgear cabinet and the driven consumer are easily accessible for everyone. For this reason, the components of the photovoltaic system can be easily damaged or manipulated.